Determination of barium and sulphate by means of tetrahydroxyquinone



Patented June 14, 1938 DETERMINATION BARIUM AND SUL- PHATE BY MEANS OF TETRAHYDROXY- QUINONE Wilburn C. Schroeder, Highland Park, N. J., assignor of one-l1alf to W. H. & L. D. Betz, Philadelphia, Pa.

No Drawing. Application June 7, 1935,

Serial No. 25,417

7 Claims.

This invention relates to the determination of barium and sulphates, especially in boiler water and in the water of air-conditioning systems, and especially by means of chemical compounds of tetrahydroxyquinone.

The production of tetrahydroxyquinone may be by means of any available process, and is particularly noted for its use in the preparation of dyes. By the use of tetrahydroxyquinone, the determination of barium and/or sulphate is made much easier and faster than by the methods heretofore practiced.

It has long been known that by the use of certain chemical compounds it is possible by titration to determine the quantity of barium and/or sulphate in a given solution, and that the end point of the titration is denoted by a definite color change in the compounds employed. It is also known that some of the compounds which are suitable for such purpose are unstable when in solution, and consequently cannot be put in solution and added to the sample to be analyzed unless the solution is comparatively fresh, so that it becomes necessary to make up fresh solutions at frequent intervals.

As the result of experiments leading up to and proving the practicability of the present invention, it has been found that the known compounds which give the desired color change, and which are relatively unstable in solution, may be mixed with various other chemical compounds (or elements), and that the resulting mixture or compound will remain stable for at least one year.

It has furthermore been found that the second 5 group of chemical compounds may be so selected that they will not interfere with the determination of barium and/or sulphate by the first compounds. In fact, it has been found that while the color-changing compounds dissolve with some difiiculty when alone, the presence of one or other of the second group of compounds insures their entering into solution readily.

The first group of indicating compounds, which give a color change at the endpoint of the titration consists in such compounds as the di-sodium,

potassium, ammonium and other salts of tetrahydroxyquinone, and/or rhodizonic acid, while the second group of compounds which act as fillers for the first, and aid the first in entering into solution, consist in such substances as sodium or potassium chloride or in fact any other chemical substance or element, which does not interfere with the determination of barium and/or sulphate, and which does not destroy or alter the color-changing properties of the compounds used 7 to indicate the endpoint.

As an example of the operation of the improved process, if even a small quantity of di-sodium, potassium, ammonium, or other chemical compound or salt of tetrahydroxyquinone is added to a solutioncontaining sodium or other sulphate, such as a sample of boiler water or the water used in air-conditioning systems, a satisfactory point.

More specifically, we can take 25 cc. of boiler or other water filtrate in an Erlenmeyer flask,

to which is added a few drops of phenolphthalein indicator, and sufficient N/50 hydrochloric acid (or dilute sodium hydroxide, if necessary) from a burette to just neutralize the same to the phenolphthalein endpoint, that is, until the acidity reaches a pH value of between 4.0 and 10.0, but preferably of approximately 8.3 at which value the desired color change best takes place. this sample as thus prepared is added to cc.

of ethyl alcohol, or ethyl alcohol denatured with 5% to 10% of methyl alcohol (U. S. Denaturant Formula No. or 3*), acetone, isopropyl alcohol,

or other diluents, such as will serve to reduce the solubility and/or to increase the rate of precipitation of the barium sulphate.

To the resulting compound or mixture is then added approximately 0.25 to 0.35 gram of dry tetrahydroxyquinone indicator (the indicator consisting of a pulverized mixture of one gram of the sodium salt of tetrahydroxyquinone and approximately 300 grams of potassium chloride), and the substances whirled in the Erlenmeyer flask, so as to dissolve and equally distribute the tetrahydroxyquinone throughout the liquid mass, 1 giving the sample a yellowish coloration. The standard barium chloride or equivalent solution, approximately 0.03 normal, is then added several drops at the time, with constant whirling of the flask until a brownish color begins to form.

This titration must be made with as much light as possible, in order to detect the endpoint, the appearance of the brownish cast not being at the endpoint, but indicating the approach of the same.

From this stage, continue .to add the soluble barium salt two or three drops at the time, until there is a predominance of red over the yellow in the solution. This is to be taken as the endpoint, as soon as the red appears evenly distributed throughout the body of the liquid, and not merely as spots of color.

From the total number of ccs. required for the titration subtract 0.1 cc. to allow for a blank in the titration. Some practice is required with this titration to secure uniformly efficient results, but the method is very accurate and the technique involved may be readily acquired.

The concentrations, weights and volumes hereinbefore mentioned, for the sample, for the indicator compound, for the neutralizing acid, for the titrating solution, for the pH value, or other specific condition, may be varied through wide limits to best meet the conditions and requirements of each determination or sample to be analyzed. Various chemical compounds which are equivalent to those specifically named and cited may be substituted without interfering with the determination. It is to be understood that the use of the ethyl alcohol, or ethyl alcohol denatured with methyl alcohol, or acetone, or isopropyl alcohol, or other diluents, are suggested in order to increase the speed and convenience of the titration, and that furthermore if desired the titration may be carried out without the useof such diluents. It is also to be understood that it is quite possible to apply this method to any compound of sulphate which is in solution, or can be put in solution by any chemical, thermal, mechanical, electrical, or physical means, having in mind the presence and determination of sulphate even in such substances as cement, steel, coal, oil, etc.

With reference to the determination of sodium or other sulphate, by the use of the di-sodium or potassium salt of tetrahydroxyquinone, such sulphate as may be present in the sample may be directly titrated as hereinbefore described, that is, starting with the color yellow and going to red, or a reverse titration may be made by starting with the endpoint, as indicated by the color red, and proceeding backwards to the yellow.

The procedure for the analysis of barium contained in the soluble barium salt consists in measuring the desired volume of solution into a beaker and diluting to approximately 50 cos. The sample is neutralized to the phenolphthalein endpoint, then 0.15 to 0.35 gram of the dry tetrahydroxyquinone indicator (consisting of a pulverized mixture of one gram of the sodium salt of tetrahydroxyquinone and approximately 300 grams of potassium chloride) is added with stirring, followed by the addition of 15 cc. of ethyl alcohol. This sample is titrated with 0.05 normal potassium sulphate until the reddish brown color has disappeared and a yellow color is apparent. It is necessary to add the potassium sulphate solution drop by drop with constant stirring to allow the barium sulphate to precipitate. When the endpoint is obtained, one or two drops must be added and the solution thoroughly stirred before the next addition of the potassium sulphate solution is made.

It is to be noted that this determination of barium may be carried out in neutral or acid solution. If carried out as directed above, the endpoint is a change from reddish brown to yellow. If, however, to the 50 cc. sample approximately 2 cc. of 0.4 normal hydrochloric acid is added, after the tetrahydroxyquinone indicator has been added and the barium salt of the tetrahydroxyquinone has precipitated, the color change is from reddish brown to colorless. Since each cc. of 0.05 N potassium sulphate used for the titration is equivalent to 6.87 milligrams of barium, it is suggested that the barium solution under consideration be of such strength as will require approximately 10 cc. of the 0.05 normal potassium sulphate.

This method for the determination of barium may be applied to any compound of barium, which may be put in solution by any means whatsoever, and it is not necessary except for the sake of convenience and speed, that the diluents such as ethyl alcohol be added to the sample. All concentrations, Weights, volumes, and acid or alkaline values may be varied to best meet conditions of each determination. Various chemical compounds which are equivalent to those specifically named may be substituted without interfering with the determination.

Supplementing the foregoing description of the improved method, and a specific example of the operation of the same, it should be understood that the di-sodium, potassium and other salts of tetrahydroxyquinone are unstable, and slowly but eventually decompose if kept in a simple solution. However, if they are mixed in the dry state with potassium chloride or any of the other substances above mentioned, which do not interfere with the analytical determination, they will not decompose under ordinary conditions, but will in addition accelerate the solution of the color-indicating tetrahydroxyquinone salt in the sample being tested.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:-

1. A stable preparation comprising a dry mixture of an alkali salt of tetrahydroxyquinone and an alkali metal chloride, said salts being adapted to be dissolved together for use as an indicator for the presence of barium.

2. A stable preparation comprising a dry mixture of approximately 1 gr. of an alkali salt of tetrahydroxyquinone and approximately 300 grs. of potassium chloride, said salts being adapted to be dissolved together for use as an indicator for the presence of barium.

3. The method of determining the amount of sulphate in a given solution which consists in substantially neutralizing an aqueous solution containing sulphate, dissolving tetrahydroxyquinone indicator containing an alkali salt of tetrahydyroxyquinone and an alkali metal chloride, and then titrating the solution with a barium compound until a different coloration appears.

4. The method of determining the amount of sulphate in a given solution which consists in substantially neutralizing an aqueous solution containing sulphate, adding from 20 cc. to 25 cc.

of ethyl alcohol, dissolving approximately 0.25 gr.

to 0.35 gr. of tetrahydroxyquinone indicator therein consisting of a pulverized mixture of 1 gr. of a salt of tetrahydroxyquinone and approximately 300 grs. of potassium chloride to give the solution a yellowish coloration, and then adding standard barium chloride solution until a reddish coloration begins to appear.

5. The method of determining the amount of barium in a given solution which consists in substantially neutralizing an aqueous solution containing barium, dissolving therein an indicator containing an alkali salt of tetrahydroxyquinone and an alkali metal chloride, titrating the resulting solution with standard solution of sulphate of an alkali metal until the characteristic reddish color disappears.

6. The method of determining the amount of sulphate in an aqueous solution which comprises adding an excess of standard barium chloride solution to said aqueous solution, substantially neutralizing said aqueous solution, dissolving therein an indicator containing an alkali salt of tetrahydroxyquinone and an alkali metal chloride, titrating the resulting solution with standard solution of sulphate of an alkali metal until the characteristic reddish color disappears.

'7. The method of determining the amount of barium in a given solution which consists in substantially neutralizing an aqueous solution containing barium, then dissolving approximately 0.15 to 0.35 gr. of tetrahydroxyquinone indicator therein consisting of a pulverized mixture of approximately 1 gr. of a salt of tetrahydroxyquinone and approximately 300 grs. of potassium chloride to produce a reddish brown coloration, adding approximately 15 cc. of denatured alcohol and approximately 2 cc. of 0.4 normal hydrochloric acid, titrating the resulting solution with standard potassium sulphate until the reddish coloration disappears.

WILBURN C. SCHROEDER. 

